Engineering the TiO_x Overlayer on Ni Catalyst to Balance Conversion and Stability for Methane Dry-CO₂ Reforming

Abstract

Ni-supported catalyst is a viable system to convert methane and carbon dioxide into syngas through methane dry reforming, with the main drawbacks of its fast deactivation being sintering and coking. Here, we developed methods to engineer a TiO x overlayer on Ni/TiO 2 catalysts to shield the catalyst against sintering and coking while preserving the Ni accessibility and, thus, conversion. These methods involved altering TiO 2 crystal phases, pretreatment, and reaction conditions in the reforming stage. Through characterization, testing, and operando spectroscopy, we found that the TiO x overlayer with incomplete Ni coverage maintained a balanced conversion and stability by quenching the sintering and coking. Conversely, thick or nonexistent overlayers led to lower conversions or faster deactivation. The formation of TiO x overlayer increased the CO 2 activation capacity and oxygen mobility and protected Ni from sintering by its shield function. At the same time, the reaction pathways remained unchanged despite the TiO x overlayer with different morphologies.

Combined Methane Cracking for H2 Production with CO2 Utilization for Catalyst Regeneration Using Dual Functional Nanostructured Particles

“…For the Al 2 O 3 -containing samples (Figure a), the Al 2p peaked at 73.0 eV, and the Ni 3p 1/2 peak and Ni 3p 3/2 peak were at 69.1 eV and 64.7–66.4 eV, respectively. In the Ni 2p spectra (Figure b), peaks with a binding energy at around 851.0 eV corresponded to metallic Ni (Ni 0 ), ,,, while peaks at around 854.5 and 872.0 eV were attributed to Ni 2p 3/2 and Ni 2p 1/2 of Ni 2+ oxidation states, respectively. ,,,− In the Ce 3d spectra (Figure c; for the sample containing CeO 2 ), the peaks labeled as u (899.0 eV), u ″ (906.2 eV), and u ″′ (915.0 eV) corresponded to the 3d 3/2 of Ce 4+ oxidation states, while peaks labeled as v (878.5 eV), v ″ (887.1 eV), and v ″′ (896.5 eV) were associated with the 3d 5/2 of Ce 4+ oxidation states. ,, On the other hand, peaks labeled as u ′ (901.0 eV) and v ′ (881.0 eV) corresponded to the 3d 3/2 and 3d 5/2 of Ce 3+ oxidation states, respectively. ,, By calculation, the fraction of Ce 3+ in Ce compounds (i.e., defined as Ce 3+ /(Ce 3+ + Ce 4+ )) was found to be 17.6, 18.0, 18.3, and 17.9% for 10Ni/1Ce, 10Ni/5Ce, 10Ni–1Ce/5Al, and 15Ni–1Ce/5Al, respectively. The results indicate the formation of oxygen vacancies (i.e., for the charge balance of Ce 4+ to Ce 3+ ) during the aerosol-based synthesis .…”

“…The hydrogen generated through this method reflects the combination of blue and green characteristics owing to its carbon capture capacity (blue) and its lack of CO 2 emissions (green) . Knowing that uncatalyzed methane decomposition exhibits very slow kinetics at temperatures below 1000 °C, utilization of a solid catalyst is essential, allowing this reaction to be initiated efficiently at a relatively lower temperature. , Among the transition metal-based catalysts, nickel is recognized as one of the most efficient in hydrocarbon cracking. ,,− Considering that unsupported nickel is prone to sintering at high temperatures, the use of a support material is necessary. , Significant efforts have been dedicated to developing straightforward and effective synthesis methods for producing suitable Ni-based supported catalysts to facilitate methane decomposition. The maximum H 2 yield (in terms of CH 4 conversion; TOF CH 4 ) ranging from 6.02 to 38.15 h –1 was achievable in a temperature range of 550–900 °C by using Ni-based catalysts. − …”

Enlarging the Three-Phase Boundary to Raise CO2/CH4 Conversions on Exsolved Ni–Fe Alloy Perovskite Catalysts by Minimal Rh Doping

“…The continuous escalation of anthropogenic carbon dioxide (CO 2 ) emissions has aroused worldwide concern due to the global climate warming issue. , Meanwhile, natural gas extraction from shale rock has garnered attention for converting methane (CH 4 ) into valuable chemicals . The dry reforming of methane (DRM) can simultaneously convert these two atmospheric greenhouse gases into syngas, which is regarded as the pivotal footstone for processes such as Fischer–Tropsch synthesis (FTS) or carboxylation. − Among the various catalysts explored, nickel (Ni) stands out due to its high CH 4 dissociation ability and cost-effectiveness, making it a promising DRM catalyst. − …”